1. Field of the Invention
The present invention relates to a substrate for a display device, a method for repairing the same, a method for repairing a display device and a liquid crystal display device and, more particularly to a substrate for a display device which is suitably used in direct-vision type liquid crystal display devices such as a liquid crystal color television and projection-type liquid crystal display devices such as a liquid crystal projector, a method for repairing the same, a method for repairing a display device and a liquid crystal display device.
2. Description of the Related Art
As examples of liquid crystal display devices, there are color liquid crystal display devices including an active matrix (hereinafter, referred to as “AM”) substrate having a plurality of switching devices such as thin-film transistors (hereinafter, referred to as “TFTs”) formed thereon, a CF substrate having a color filter (hereinafter, referred to as “CF”) layer of a plurality of colors and a common electrode which are laminated in order thereon, and a liquid crystal layer interposed between both the substrates. The AM substrate includes a plurality of pixel electrodes arranged in a matrix shape, the CF substrate includes a common electrode opposing to the pixel electrode and an alignment of the liquid crystal is controlled with the field intensity between both the electrodes.
In the event that a conductive foreign substance is intruded between the pixel electrodes formed on the AM substrate and the common electrode formed on the CF substrate in a conventional liquid crystal display device thus resulting in an electrical short-circuiting (hereinafter, referred to as “vertical leakage”), the electric potential difference between the pixel electrodes and the common electrode is nulled, thereby causing a liquid crystal molecule at the portion to be unoriented. This will cause pixel defects such as bright spots in normally-white type apparatuses (which display a white color when a voltage is not applied) and black spots in normally-black type apparatuses (which display a black color when a voltage is not applied). Such the vertical leakage is caused by a conductive foreign substance adhered during TFT processes, CF processes, liquid crystal processes and, in order to find the vertical leakage, it is necessary to conduct lighting inspections at the state where the TFT and CF panels are attached to each other. Furthermore, the probabilities of occurrences of the vertical leakage have been increased with increasing sizes of pixels in association with the increasing sizes of display devices which have been required in recent years and with decreasing cell gaps for realizing high-speed responses. With increasing probabilities of occurrences of the vertical leakage, the yields of panels have been reduced.
The pixel configuration of a conventional liquid crystal display device will be described by exemplifying the pixel configuration of an MVA (Multi-domain Vertical Alignment) type liquid-crystal displaying mode, on the basis of drawings.
MVA type display device employs a band-shaped component (an alignment control protrusion) provided on the CF substrate and a cut-out (a slit) in the pixel electrode provided on the AM substrate which are alternately arranged on these substrate surfaces and generate liquid crystal alignments having directions of director which are different from one another by 180 degrees by using the aforementioned component and the slit as boundaries for dividing the alignment of vertical-alignment type liquid crystals, wherein a plurality of domains having director directions which are different from one another by 180 degrees are provided within a single display pixel region to provide uniform visual angle characteristics (refer to, for example, JP-P No. 11-242225). As described above, the pixel electrode of an MVA type display device is provided with a plurality of slits for restricting the alignment of a liquid crystal molecule, and, for example, as illustrated in FIGS. 1-2, an electrode connecting portion between electrode slits (a pixel-electrode connecting portion) 12 is provided in order to provide a continuous electrode pattern within the pixel. In general, the pixel-electrode connecting portion 12 is provided around a pixel electrode 9 and an alignment defect (a disclination) and a light leakage near a data-signal wiring (signal line) 4 is collectively shielded by a light-blocking film called a black matrix provided on the CF substrate for alleviating reduction in the aperture ratio. However, a configuration of conventional MVA type pixel electrode has not enabled repairing a pixel suffering from the vertical leakage thus resulting in a defect on a pixel-by-pixel basis and therefore have been susceptible to improvements.
There is another aspect of an MVA type display device in which a protrusion for controlling alignment is provided on the AM substrate while a slit is provided in the electrode on the CF substrate. In this case, as illustrated in FIGS. 4-2, for example, the opposed electrode (common electrode) on the CF substrate is provided with a slit and the opposed electrode is continuous with the adjacent pixel. Therefore, in order to cut away a portion suffering from the vertical leakage, it is necessary to cut away the surrounding area of the pixel electrode having the portion. Therefore, there has been room for minimizing the to-be-cut portion and making the portion suffering from the vertical leakage to be a minute defect which is difficult to recognize as a defect.
There have been disclosed liquid crystal display devices capable of coping with occurrence of the vertical leakage by having a slit portion formed in the pixel electrode, in relation to a conventional technique for repairing a pixel defect (refer to, for example, JP-P No. 2000-221527, JP-P No. 2004-93654, and JP-P No. 2001-83522). However, the liquid crystal display devices in JP-P No. 2000-221527 and JP-P No. 2004-93654 utilize a slit provided at a portion outside of a light-blocking film where there has originally existed no slit and the pixel electrode is cut off resulting in expansion of the slit region. Therefore, these liquid crystal display devices have been susceptible to improvement for maintaining the display quality without inducing an alignment defect. Furthermore, there is a possibility of cutting off a data-signal wiring during cutting away a defective portion which may induce a line defect and, therefore, these apparatuses have been susceptible to improvements.
Further, with the liquid crystal display devices in JP-P No. 2000-221527 and JP-P No. 2001-83522, in the event of occurrence of a defect near the storage capacitor, if the pixel electrode on the portion is cut away, then the pixel electrode constituting the storage capacitor is cut away. Therefore, the apparatuses have been susceptible to improvement for causing the storage capacitor to work sufficiently to maintain the display quality even after repairs.
Further, the liquid crystal display devices in JP-P No. 2000-221527, JP-P No. 2004-93654 and JP-P No. 2001-83522 employ a configuration for supplying a drain electric potential to the pixel electrode through a contact hole near a transistor, and therefore they have been susceptible to improvement for enabling partially repairing the pixel electrode in the event of the vertical leakage between the transistor and the storage capacitor wiring. Further, they have been susceptible to improvement for sufficiently coping with, in addition to the vertical leakage, defect modes such as an electrical short-circuiting between the drain extracting electrode and the storage capacitor wiring (Cs) (hereinafter, referred to as “D-Cs leakage”) and the electrical short-circuiting between the data-signal wiring and a capacitance electrode formed on the storage capacitor wiring.